Platelet aggregation plays an important role in thrombosis and blood coagulation. When a blood vessel is injured, platelets are activated, for example, by collagen under the vascular endothelium, so that binding of fibrinogen to the platelets, i.e., platelet aggregation is caused, resulting in thrombosis. As the final step in platelet aggregation, there is a step in which glycoprotein IIb/IIIa receptor on the platelet surface is activated and then bonded to fibrinogen. Therefore, an inhibitor capable of preventing the combination of glycoprotein IIb/IIIa receptor and an adhesion protein such as fibrinogen is considered useful for preventing thrombosis and blood coagulation.
It is considered that in the binding of fibrinogen to glycoprotein IIb/IIIa receptor, the amino acid sequence Arg-Gly-Asp-Ser (hereinafter referred to as RGDS) portion on fibrinogen is an active site. Therefore, RGDS analogues have been developed as antagonist for glycoprotein IIb/IIIa receptor. They are expected as agents for suppressing metastasis of cancerous cells.
As such competitors, peptide derivatives containing an amino acid sequence Arg-Gly-Asp are known. They, however, are not sufficient in ease of oral absorption, etc. when used as a pharmaceutical.